Today's Message Index:
----------------------
1. 02:17 AM - Re: Contactors (Peter Pengilly)
2. 05:45 AM - Re: Contactors (Sacha)
3. 06:55 AM - Re: Trusting a chargers reputation, what an idiot! (user9253)
4. 07:19 AM - Re: Watts on resistors (Carlos Trigo)
5. 02:11 PM - Re: Contactors (Sacha)
6. 05:36 PM - Re: Aviation intercom (R. curtis)
Message 1
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There is a potential problem in using only the starter contactor to
switch the starter motor power - those contactors are known to
occasionally weld themselves together. In that case, with only the
starter contactor switching power to the starter, there is then no way
of disengaging it from the running engine until the battery is flat (if
that ever happens as the starter is now a generator). In the UK the
authorities insist that a light is installed in the panel warning the
pilot the starter remains energised, as there have been several
accidents. The engaged starter saps a large amount of power from the
engine and gets very hot, with unpleasant consequences.
If a modern starter with a piggy-back solenoid is fitted, to avoid the
master relay handling the starting current, the jumper that normally
energises the solenoid can be brought into a cockpit switch to disable
the starter if the the starter contactor does weld on. A small
additional parts count, but the switch never does any switching except
in emergency.
Peter
On 01/11/2013 17:44, Sacha wrote:
>
>
> On Nov 1, 2013, at 13:37, "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
wrote:
>
>>
>> At 12:10 AM 11/1/2013, you wrote:
>>>
>>> I use automotive "cube" relays (one for the master relay, one for alternator)
rated at 70A. They are light and consume less than 300mA each. Is there a reason
not to use them? The only potential drawback I'm aware of is that they
can break the contact if subject to violent shocks. But loosing panel power for
a few milliseconds doesn't seem such a big issue (the autopilot does reset but
then in such violent turbulence you might be hand flying the thing in any case,
and the GNS430 doesn't even notice any absence of power that lasts that little).
>>>
>>> Are there other risks I am not considering here? This is a VFR only machine
and I'm a low time PPL so not the most experienced in these matters.
>> The legacy battery contactor is tasked with
>> carrying normal operating loads usually in
>> the tens of amps but predicated on getting an
>> engine started . . . loads of perhaps 200A.
> Ah. Ok now I understand your previous question. In my case the fat wire to the
starter contactor is always hot. The master just activates the coil circuit.
>
> I now know this is against conventional design where master OFF is supposed to
correspond to max darkness. In my case the total length of fat (positive) wire
is approx 50cm (20"): battery to starter contactor to starter motor.
>
>
Message 2
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There is a potential problem in using only the starter
contactor to switch the starter motor power - those contactors are known to
occasionally weld themselves together. In that case, with only the starter
contactor switching power to the starter, there is then no way of
disengaging it from the running engine until the battery is flat (if that
ever happens as the starter is now a generator). In the UK the authorities
insist that a light is installed in the panel warning the pilot the starter
remains energised, as there have been several accidents. The engaged starter
saps a large amount of power from the engine and gets very hot, with
unpleasant consequences.
Good point, I hadn't thought of that failure mode.
If a modern starter with a piggy-back solenoid is fitted, to
avoid the master relay handling the starting current, the jumper that
normally energises the solenoid can be brought into a cockpit switch to
disable the starter if the the starter contactor does weld on. A small
additional parts count, but the switch never does any switching except in
emergency.
You're speaking about the solenoid on the starter motor? I don't recall
seeing any external jumper there (the engine is a Rotax 912). I'll have a
check next time I'm down at the hangar.
Message 3
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| Subject: | Re: Trusting a chargers reputation, what an idiot! |
> the battery is 13.4 and the MGL Efis shows supply voltage as 12.9. I have checked
all feeds and connectors, but cannot isolate the voltage drop....
Subtracting 12.9 from 13.4 equals 0.5 volts which is the voltage drop across a
diode. Is the MGL EFIS powered through an E-Bus diode? What happens when the
E-Bus alternate feed path (if installed) is turned on?
Joe
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=411967#411967
Message 4
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| Subject: | Watts on resistors |
Many thanks to all who responded.
Apart from the aplication itself (resistor already installed), it's always
a pleasure to learn something every day.
And this list is one of the best to this purpose.
Best
Carlos
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Robert L.
Nuckolls, III
Sent: sexta-feira, 1 de Novembro de 2013 15:40
Subject: Re: AeroElectric-List: Watts on resistors
At 09:21 AM 11/1/2013, you wrote:
<trigo@mail.telepac.pt>
Bob and all
The VP-X Pro installation manual recomends, in order to have Volt indication
from the Aux Batt, to connect the + terminal to a certain pin in the box,
trough a 1Kohm - 1W resistor.
Problem is that I can only find 1Kohm - 2W resistor. So, to learn something
else today, can someone please explain if there is any problem if I use the
2W instead of 1W resistor.
(Please don't answer indicating a source for 1W resistors...)
That's an easy one.
The resistor is a substitute for a fuse. Further,
it's called out as 1-watt for mechanical convenience
and robustness. Examples:
Some years back I suggested that the most valuable
and often least accessible data point for diagnosing
an alternator problem is to watch FIELD VOLTAGE
behavior while putting an alternator through
its paces.
I published this little feature in Z-23 suggesting
a permanently attached wire PROTECTED by a resistor
leading from the alternator field to some handy point
in the cockpit.
Emacs!
A fuse would be okay too. A 1/4 watt would work but 1/2
watt was mechanically more robust, 1w would have
been better yet. So as long as you don't mind a larger
'lump' in your battery sense lead, a 2W resistor is
okay as well.
http://tinyurl.com/kyc6tq6
I think it was here on the List that I once suggested
a tubular, 10-watt wire wound resistor with flag
terminals as a suitable enclosure for a reed switch
current sensor.
Emacs!
The 'jeep' was to put lead wires on the reed switch
then epoxy into place down the center of the tubular
resistor. Then wind an excitation coil around the
center of the resistor over the reed. Calibrate
closure current for the reed by adjusting coil
turns.
In this case, the actual value of the resistor
wasn't critical . . . just needed to be high
enough not to adversely affect current through
the the coil. The resistor became a robust
'housing' for the current sense relay offering
a convenient terminals to tie off ends
of the coil.
These are but two examples of many where the
designer's 'sizing' of a component may not
have obvious foundation in the original
design goals for the part.
Bob . . .
Message 5
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>> If a modern starter with a piggy-back solenoid is fitted,
>> to avoid the master relay handling the starting current, the jumper that
>> normally energises the solenoid can be brought into a cockpit switch to
>> disable the starter if the the starter contactor does weld on. A small
>> additional parts count, but the switch never does any switching except in
>> emergency.
>
> You're speaking about the solenoid on the starter motor? I don't recall
> seeing any external jumper there (the engine is a Rotax 912). I'll have a
> check next time I'm down at the hangar.
I couldn't find anything there unfortunately. The starter motor just has one terminal
for the fat positive wire.
Message 6
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| Subject: | Re: Aviation intercom |
Does anyone have the schematic or Manual for the WGA Model AIR-1177 Aviat
ion Intercom System=3F I am trying to figure out the input and output jacks
on the box. I intend to mount it in a panel along with an isolation amp.
The box has on-off volume and squelch controls. There are 3 cables comi
ng out of each side of the box, one side for Pilot and the other for Copilo
t. 2 of the cables are mic and headset jacks, and there is another cable wi
th a 1/4=22 plug attached, and don't know where this gets plugged into. Also
there are 3 small jacks on the end of the box marked EXP, COPILOT, AUX. D
on't know what these are for either.
I called the company some time ago and got some rather arrogant non ans
wers so this is why I decided to ask on the list if anyone has any experien
ce with this device.
Any assistance appreciated.
Roger
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